Heating systems of this nature are, at present, often used to generate electrical energy from waste heat. It is desirable that a generally constant heating pressure or heating temperature is maintained in the boiler. Because the access to waste heat often varies, it is convenient to control the rate of flow of the medium through the expansion device so as to establish desired boiler conditions.
The rate of flow of the medium through the expansion device can be controlled effectively by controlling the number of revolutions. However, the control arrangement for carrying out this control involves high investment costs, which cannot be readily justified economically.
Alternatively, this control can be achieved by throttling the input flow with the aid of a throttle valve or choke. However, such throttling of the flow lowers the efficiency of the system very significantly.